The past year has revealed a remarkable capacity for individuals to incur personal costs for the benefit of the common good as we confront a global pandemic – such as volunteering as front-line workers, donating protective materials and supplies, and adhering to quarantine policies [1]}, [2]}. The question of why some societies, but not others, have readily met the challenge of costly cooperation for the common good reflects a classic problem in evolutionary theory: why would an individual forgo her own interests to help strangers? Understanding the spread and maintenance of cooperation is now recognized as an important practical problem, with tangible benefits. This is especially true today, as our globe tackles collective action problems in public health, resource management, and climate change [3]}.
